1. Field of the Invention
This invention relates to circuit interrupters wherein an arc extinguishing fluid such as SF.sub.6 gas is utilized to extinguish an electric arc.
2. Description of the Prior Art
It has been a common practice in circuit interrupters using a gas having a strong arc extinguishing capability such as SF.sub.6 gas to generate a pressure difference in the gas by a suitable means and to puff the high pressure gas to the electric arc to be extinguished, thereby effecting current interruption. There has been known two types of means for establishing the above mentioned pressure difference.
One type of circuit interrupter known as the double pressure type comprises a gas filled at a predetermined pressure within a casing in which SF.sub.6 gas is also filled and a separate pressure generating apparatus for generating a high pressure, thereby obtaining the necessary pressure difference for generating a flow of the gas for arc extinction. Upon interruption, a valve disposed between the high pressure gas and the low pressure gas is opened in response to a contact opening operation to allow the high pressure gas to flow toward the arc, thereby blowing out the electric arc. With this type of circuit interrupter, the pressure generating apparatus for generating a high pressure and maintaining it and two pressure systems for high and low pressure gases are separately constructed, so that the overall structure of the interrupter is extremely complicated and large, rendering it uneconomical. Besides, it is disadvantageous from a practical view point in that the high pressure of the gas must always be maintained.
The second type of circuit interrupter is known as a single pressure puffer-type wherein a puffer device disposed within a gas of a few atmospheres pressure contained in a sealed casing is operated in response to the interrupting operation to generate a high pressure gas, which gas is then puffed to the electric arc to extinguish it. This type of circuit interrupter utilizes compressed gas of a pressure lower than that used in the double pressure type, so that designing of a practical casing structure is easier. However, the circuit interrupter requires a mechanical pressure generating device such as a puffer device operable in response to the interrupting operation. The puffer device requires a stronger driving force for a higher input electrical power and a higher interrupting current, inevitably resulting in the requirement for a powerful operating mechanism in a large capacity circuit interrupter. It is also proposed to assist the large operating mechanism with an electromagnetically operated puffer device, but this operating mechanism is also disadvantageous in that it is large-sized, complicated in structure, not economical and not practical.